Spectral and luminescent properties of forsterite single crystals heavily doped with chromium: I. Absorption spectra

The polarisation absorption spectra of forsterite single crystals grown from a melt containing from 0.015 to 0.97 wt% of chromium are studied. Most of the crystals were grown by the Czochralski method under standard oxidation conditions (1.4–2.4 vol % of oxygen). Some crystals were grown in the atmosphere with a higher content of oxygen (~12 vol %) or in the neutral atmosphere (100% of Ar). Crystals grown from a melt containing more than 0.6 wt % of chromium exhibited the saturation of absorption of Cr⁴⁺ ions. The maximum absorption coefficient of Cr⁴⁺ ions at 1064 nm was ~3.2 cm^-1. The relative content of Cr³⁺ ions also increased (approximately by 70% in the range studied) with increasing the doping level. The relative content of Cr³⁺ ions in a crystal grown in the atmosphere with a high content of oxygen (~12 vol %) was approximately lower by a factor of 1.5 than that in a crystal grown in the standard oxidation atmosphere.